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2nd harmonic frequency on narrow band sensors?

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In short, does 2nd harmonic frequency work for a narrow band sensor or should it be used for a wideband sensor only?

Long story here:

I've recently did a 1ZZ to 2ZZ swap on a Lotus Elise with a Syvecs ECU installed. The swap itself was easy as Lotus uses the same harness for both engine where the additional connectors required for the 2ZZ are already there, just tucked away unused.

The 1ZZ uses an old single wire M10 screw in type knock connector but it is not connected as Lotus does not use knock detection for the 1ZZ engine. For the 2ZZ engine, there are two variants for the 2ZZ knock sensor. Most 2ZZ also uses the old single wire type knock sensor while certain newer 2ZZs uses the two wire doughnut style knock sensor. My 2ZZ came from a Celica so it uses the old type.

However, the Lotus 2ZZ uses the two wire type so to make it work, I modified the connector and connected up the single wire knock sensor. The problem I have right now is the signal from the knock sensor appears too be too loud. Even when set to the lowest gain level, it is still over Syvec's recommended level (recommendation was 3% at idle and I was getting 6-8%) and it is detecting knock at places where there shouldn't be.

I wanted to try the 2nd harmonic frequency to see whether it would make any difference but I am not sure it would be accurate at all given the narrow band nature of the sensor. Will the sensor be able to detect knock in the 2nd harmonic frequency?

im not sure what effect or result you will get other than trying the 2nd harmonic and seeing what it does. but this is the system i use and how it works it maybe of some use to you The Knock Audio function is a feature to help identify knock sensor frequency. It is able to analyze the audio output of the Knock Amplifier and help determine the correct frequency filter for your knock sensor. The Knock Audio function does this by using the audio output from the Knock Amplifier and inputting it into your PCs sound card. The audio signal is then visually represented on the screen to help identify the frequency at which knock is being measured.

·Setting up Knock Audio

·Using Knock Audio

·Detecting Engine Knock

·Knock Audio Fault Finding

Setting up Knock Audio

1.Connect the Knock Amplifiers (or KnockBlock) audio output to the PCs microphone input using a double ended 3.5mm audio cable.

2.Open the Knock Audio window (PCLink > Tuning > Knock Audio).

3.Select the Audio Input Device you have the Knock Amplifier connected to.

4.Select the Waterfall draw rate. This controls the rate at which the Knock Audio visual display is re-drawn at, set this to fast. If you encounter problems with your PC being too slow drop the rate back to medium or slow. Press OK.

"Knock Audio - Properties"

Using Knock Audio


Knock can potentially damage an engine, extreme care must be taken. Link will take no responsibility for any damage caused to an engine when configuring Knock Audio or Knock Control. It is the tuners responsibility to take all measures to protect the engine and users.

1.Make sure the display mode is set to Sampled. Start your engine up, and make sure the ignition timing is conservative. Click the record button in the Knock Audio window and increase engine RPM to above idle (1500 to 200 RPM on most applications). Adjust the volume slider to the point where the peaks of the signal are reaching the area between the first and second line from the center.

"Knock sampled example"

2.Change the display mode to Waterfall. Click the stop button to stop the image recording. Look at the display and compare it to the two images below to help determine if the knock sensor type is a narrow-band or wide-band sensor. Adjusting the contrast can make the image easier to interpret.

Narrow-band Knock sensor

"Knock Narrowband waterfall"

A narrow-band knock sensor will display as a thin band of colour occurring at a particular frequency. A lot of factory knock sensors are narrow band sensors as they are selected to match the knock frequency of the engine.

If the Knock Audio waterfall display has a single band of colour, look at the y axis of the waterfall display to determine the frequency it occurs at. In this example image the frequency is at approximately 7 kHz.

The frequency filter on the Knock Amplifier or Link ECU can now be setup to match the frequency determined.

Note: Some narrow-band knock sensors, known as second harmonic knock sensors, operate at a frequency above 10 kHz. To expand the viewable frequency range in the waterfall display drag the top or bottom edge of the Knock Audio window.

Wide-band Knock sensor

"Knock Wideband waterfall"

A wide-band knock sensor will cause the Knock Audio waterfall display to show an image that contains colour (noise) at a wide range of frequencies. This makes it difficult to determine the correct frequency filter to select when setting up a Knock Amplifier or Link ECU.

There are two solutions to this problem. The first solution is best as it does not risk engine damage. Use of the second method is at the tuners risk.

·Use the calculation method for determining the knock frequency of the engine:

Knock Resonant Frequency (Khz) = 1800/(3.14 * piston diameter in mm)


·Take a screen capture of the waterfall display with the engine running conservative ignition timing. Then record another waterfall display image with the timing very momentarily advanced enough to cause light engine knock. Compare the two waterfall display images, the second image should have colour (noise) in a frequency range the first image does not. Where this colour occurs is the frequency range the engine knock is occurring at.

The frequency filter on the Amplifier or Link ECU can now be setup to match the frequency determined.

Detecting Engine Knock

If engine knock occurs this will be visible in the waterfall display as the colour pink, the intensity of the knock will correspond to the amount of pink that shows in the image. In order for the engine knock to show correctly the contrast slider must be adjusted so that normal engine noise does not show up as pink. The image below is an example of engine knock being present in the waterfall view.

"Knock Wideband w knock waterfall"

Right clicking on an area in the waterfall view and selecting 'Show FFT for point' will cause that 'vertical slice' of the waterfall view to be displayed as a Fast Fourier Transform image. This is useful to help analyse the noise that Knock Audio is receiving. The FFT image below is from the point where pink is showing in the image up. As you can see there in the FFT image, there is a sharp spike in noise intensity in the 5 to 7 kHz range.

"Knock Audio FFT"

Holding the shift key while pressing the left or right arrow key will cause the FFT view to move one 'vertical slice' of the waterfall view to the left or right. This is useful when trying to identify a very brief period of engine knock.

Knock Audio Fault Finding

·If you can not obtain a suitable level of signal in the Sampled view by using the Knock Audio volume slider you may need to adjust the Knock Amplifier or PCs main volume control.

·If you can not obtain a signal in the Knock Audio confirm that the signal is reaching the PC correctly by listening for the engine noise through your PC speakers. On some versions of windows this involves changing your microphone properties in control panel.

·If you have a large spike in the FFT view that is always present (even without the engine knocking) it is possible that you are picking up external noise. Check the Knock system wiring, confirming that the shielding, GND and signal are connected correctly. See Knock Inputs for more detail on knock sensor wiring.

·Some older PCs and laptops have inferior sound-cards that are unable to produce the volume or sound quality required for Knock Audio. If you are unable to resolve problems with noise try another PC or laptop.

this is from the linkecu help file

Regards ross

Hello Ross, yes I guess I could simply try using the 2nd harmonic and see what happens but my worry would be what if it still receive a sound signal but fails to pick up the frequencies generated by actual knock. I wouldn't mind trying if it is an engine that I am familiar with and I could produce some mild knock to check it but this is not.

Anyway, this is a Syvecs ECU and I've asked Syvecs about it and it seems like the S6GP knock detection does not work with a narrowband sensor at all. I guess that is probably why I am getting an oversaturated signal and have now swapped in a wideband.

Im not familiar with the 1ZZ sensor, but most of the single wire toyota knock sensors (3S, 2J etc) are high sensitivity and output very high amplitude/voltage. They do not work well with most aftermarket ECU's as they completely saturate the input.

Yes, that's exactly what I am experiancing. Thank you for the confirmation Adam.

Given what you have said, I think I have previously used a stock knock sensor on a 3SGTE with a G4+ PNP. It was ages ago so I cannot remember clearly but I think low enough gain settings were available to make it work. But eventually, we also swapped in a wideband sensor.

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